Technical Field
The present disclosure relates to a radar apparatus, and specifically relates to an on-vehicle radar apparatus mounted on a vehicle to detect various targets around the vehicle.
Background Art
Conventionally, on-vehicle radar apparatuses are used to detect various targets around the vehicle and sense a risk of collision of the vehicle and the target. Such on-vehicle radar apparatuses may erroneously detect a position of target if an optical axis deviation occurs, that is, when an optical axis of a radar wave (e.g., millimeter wave, laser beam, ultrasonic wave) is deviated from a predetermined mounting direction (for example, a front-back direction of the vehicle) due to some reasons (such as changes over time). The optical axis as used herein is an axis which extends through the center of a sensing area of the on-vehicle radar apparatus.
As a technique to detect such an optical axis deviation, JP-A-H9-250970 discloses a technique using the azimuth dependence of relative speed to a stationary object.
Specifically, when a relative speed of the stationary object observed by the radar is Vs, an own vehicle speed is Vh, and an azimuth at which a target exists is θ (the azimuth in the radar coordinate system on the basis of the optical axis), they have a relationship expressed by the following equation (1), where a parameter A is a ratio of speed errors contained in the own vehicle speed Vh and the relative speed Vs, and A=1 represents a case in which no error exists.
                    [                  Math          .                                          ⁢          1                ]                                                                      Vs          Vh                =                  A          ·                      cos            ⁡                          (              θ              )                                                          (        1        )            
When the optical axis deviation (an angle of the optical axis relative to the mounting direction) is α, an apparent azimuth (an azimuth in the vehicle coordinate system on the basis of the mounting direction) θ′ is expressed as θ′=θ−α. The detected relative speeds are the same regardless of presence or absence of optical axis deviation. When taking into consideration the optical axis deviation, the equation (1) can be replaced with an equation (2).
                    [                  Math          .                                          ⁢          2                ]                                                                      Vs          Vh                =                  A          ·                      cos            ⁡                          (                              θ                -                α                            )                                                          (        2        )            
That is, in a chart plotted with Vs/Vh and the azimuth angle measurement θ, a peak value is obtained when θ=0 if there is no optical axis deviation (α=0) and the peak value is obtained when θ=α if there is an optical axis deviation (α≠0). Accordingly, the optical axis deviation amount is estimated as α.